Can you use a single wall 8” stovepipe through a metal ceiling

[Vtmbz]

I have to step in here. Retired chimney mason, seen everything, including lots of charred rafters and roofs.

Insulating wood members is considered a bad idea as it retains heat right where you dont want it. Evaporators are essentially chimney fires, its a very extreme application of fire. Many people will tell you about flames shooting up a stack eight feet above their arch, including me. As noted, it gets very very hot up there.

I set my arch up by building a square chase two feet square through my ceiling clear to the steel roof. That way i could visually inspext the whole run of pipe at all times. I cut all the roof strapping out of the two foot hole so there is nothing flamable in that section, and i can see the steel from the floor. It is enclosed so the attic space is separated. Dont fabricate a home brew pipe in this section, its just not worth the risk

In my area used Selkirk metal bestos in the size you need is common. No need to buy new. Usually half the cost at least.
One tip: keep the area where the sections join away from wood because there can be some settling of the insulating material in used pipe if it isnt pristine and carefully handled. The newer pipe probably doesnt have this problem like the old stuff did.

I did a refractory wrap with wire in one part for a while, but didnt like the idea of squirrels maybe tearing it up. I kept looking at it during a boil, and finally replaced it.

Make certain that in no case can the pipe ever come loose. I used heavy steel strapping (not pipe hanger strap) lag screws and nuts and bolts. Remember that while you are putting out chimney fire, your pan is melting.

Used mb will generally come with a roof kit designed for the purpose. I bought roof kit for a ten inch pipe and ran a7” insulated pipe through that, so there is air exchange between both as well. Lots of air space above the roof, then there is a collar that comes with the roof kit that can be siliconed when done. In my case, i dont object to a little rain because it runs clear down the stack. Above the roof, single wall pipe is fine. I use stainless pipe here. Galvanized pipe wont last long in this application. For the record, the chrome burns off the first year so shiny is out, but it doesnt rust and stays solid. I guy that in place with electric fence wire, lots of excess so i can take the stack down when wanted and reuse the wire.

Sugar houses burn down all the time around here. It sucks, so dont reinvent the wheel.

[Swingpure]

Thanks.

In my case I do not have a ceiling and my trusses in that area are five feet apart. It is open air up to the metal roof and open air above the metal roof.

I will have a brand new 36” long double wall pipe going through the metal roof. The double wall section of pipe should weigh around 35 lbs.

The one thing I have not finalized yet is how to support the double walled pipe. I was debating running two, five foot plus long, 1/4 to 3/8” flat iron on top of the cross chords of the trusses and let the double wall pipe sit on them. I was also thinking of having a piece of ceramic blanket sandwiched between the flat iron and the truss.